Femtocell base stations, which are also referred to as Home base stations or Home nodeBs or Home eNodeBs when they are implemented in 3GPP systems, are base stations with limited range, for example with a transmission radius of only 10 m, for use in indoor environments to improve coverage and capacity. Femtocell base stations have a limited range e.g. limited to a home or office area. As a consequence of this small coverage area a network employing Femtocells can reuse frequencies (or more generally resource blocks) more often and thus has increased capacity when compared to a network using larger cells.
Besides these benefits to network operators, Femtocells can also be of benefit to the end user as they can provide network coverage in areas that would be devoid of such coverage in the absence of the use of such Femtocells, for example in buildings through which propagation of an outside network is impeded. The use of Femtocell base stations is especially attractive for homes where the signal from the macro-cell may not be able to penetrate the home, for example due to difficult radio propagation conditions. In situations where a Femtocell base station provides network coverage in an area any user equipment in the covered area may establish a connection to the Femtocell base station, rather than to an also available macro-cell base station, thereby achieving improved connection. This not only helps to off-load traffic off the macro-cell but also creates more capacity on top of what the macro-cell has to offer. Reduced load on the existing macro network by offloading traffic to Femtocells helps to improve performance of the macro cell users. At the same time the capital and operating expenditure of the network operator is reduced.
Capacity improvements in the home can moreover assist network operators in rolling out competitive pricing plans e.g. unlimited usage at flat rates to compete with fixed line telephones. The use of Femtocell base stations can be incentivised. Network operators may, for example, be able to reduce call charges, possibly even to such an extent that they are free of charge to the customer, associated with the use of Femtocells, as such use will result in better performance/improvement in capacity at a cheaper price/lower usage rates. Thus both the customer and the operator may benefit from the use of Femtocells.
Femtocells are designed to be customer premises equipment. Because of the small coverage area of Femtocells a large number of Femtocell base stations may be operated simultaneously, having been deployed in an ad hoc fashion. In contrast to the manner in which traditional cellular networks are operated it may thus not be possible to carry out elaborate network planning for Femtocells.
As the cost associated with the installation of Femtocell base stations by a skilled technicians is prohibitive Femtocell base stations are moreover likely to be installed by end users, most of whom may not appreciate the technical aspects of the installation. Femtocell bases stations are consequently expected to be plug and play type devices that self configure and self optimize during setup and operation.
Once a Femtocell base station powers on, there are several tasks that it needs to perform. Firstly a network operator's networks need to be discovered and the Femtocell base station needs to register itself with a thus discovered network. Registration involves the sending of the Femtocell base stations credentials to an authentication server of a discovered network. The authentication server then authenticates the Femtocell base station. Subsequent to successful authentication, the operator's network sends initial configuration parameters. The time-tested standard TR-069 titled “CPE WAN Management Protocol” from the DSL forum, which is herein incorporated by this reference in its entirety, may be used for authentication.
The initial configuration of Femtocell base stations does not include operational aspects related to Radio Resource Management (RRM), which comprises interference management. RRM solutions in which the transmit power of a Femtocell base station is altered so as to reduce interference and independently from and without coordination with other Femtocell base stations are known.
Such standalone solutions, where Femtocell base stations act independently from each other, may not always be able to provide a stable management of radio resources. If two or more Femtocell base stations independently change operating frequency without coordination to the same new operating frequency, this new frequency is the same for two or more Femtocell base stations then the changes made by the Femtocell base stations may not have solved the interference problem. Instead the problem may have been compounded.
Networks employing Femtocell base stations that manage interference in the above described manner may work well in circumstances exhibiting sparse deployment or low levels of traffic. Such networks may, however, not perform well under dense deployment scenarios or if there is significant contention for resources. In the latter situations it may be more desirable to coordinate interference management between Femtocell base stations.